Prolonged diabetes is well known to be associated with widespread microvascular and macrovascular defects, including altered vascular reactivity and increased arterial stiffness. This pilot (R21) project will examine if these vascular changes can be detected early in the course of the disease in peripheral muscles using completely non-invasive magnetic resonance imaging (MRI) techniques, combined with simple, low-impact exercise tests. Aim 1 will examine if the transient reflex muscle hyperemia observed in healthy subjects after brief contractions is altered in patients with Type I (n=15) and Type II (n=15) diabetes compared to age/sex/weight matched control subjects (n=30). Hyperemia transients will be measured by oxygenation-sensitive changes in echo-planar MRI signal intensity (blood-oxygenation level dependent (BOLD) effect), as well as by near-infrared spectroscopy and Doppler ultrasound. Aim 2 will examine if analysis of phase-contrast MRI flow waveforms from peripheral arteries before and after exercise can yield a simple, non-invasive index of arterial stiffness in diabetic vs control subjects, Aim 3 will exploit the increase in muscle T2 after exercise as an index of functional oxidative capacity in peripheral muscles of diabetic vs control subjects. The MRI portion of this study will be accomplished during a single-session MRI-exercise test, which could be adapted for routine evaluation of peripheral vascular complications in diabetic patients.